The present invention relates to a pattern inspection system for inspecting a pattern formed on a base. The present invention is used for inspecting patterns of photomasks which are used in the production of printed circuits.
In the prior art there is a method for inspecting patterns of photomasks, wich compares a pattern to be inspected with a reference pattern by means of a microscope. This method has two limitations: (1) it is not possible for a person to measure the width of the pattern, and (2) the method requires that the two patterns be aligned. This prior art method is disclosed in, for example, the thesis "Automated Equipment for 100% Inspection of Photomasks", by K. Levy, Solid State Technology, pp. 60 to 71, May 1978.
There is another prior art method for inspecting patterns of photomasks in which pattern data consisting of electrical signals transduced from light scanning a pattern to be inspected are compared with reference pattern data converted from the design data of a photomask. This method has three limitations in that it requires a process to align the reference and scan data, the original design data for the reference pattern must be generated and a high speed computer for converting the original design data is necessary. This prior art method is disclosed in, for example, the thesis "Automatic Mask Inspection for Registration Errors and Critical Dimensions", by O'Callaghan et al., Symposium of the Society of Photographic Scientists and Engineers, February 1975.
The present invention has been proposed in order to solve the problems involved in the prior art pattern inspection methods, as set forth above, and to provide a more precise and practical pattern inspection system without using reference pattern data.
A preceding invention regarding a pattern inspection system invented by some of the inventors of the present invention was disclosed in the Japanese Patent Application Laid-open No. 53-24233. This pattern inspection system includes light scanning means for scanning a photomask pattern being tested by a light beam, means for providing information indicating the width of the pattern in the direction of scanning by detecting the light transmitted through or reflected by the photomask having the pattern, and means for providing information indicating the angle of the pattern with respect to the direction of scanning by detecting the light diffracted at the edge of the pattern. In this system, the width of the pattern is measured by combining the information indicating the width of the pattern and the information indicating the angle of the pattern. The present invention utilizes the technique of this preceding invention.